Temporary support for photographic gelatin layers and method of transferring same to permanent supports



8, 1946. s. POTTER ILITAL 2,392,503

TEMPORARY SUPPORT FDR PHOTOGRAPHIC GELATIN LAYERS AND METHOD OFTRANSFERRING SAME TO PERMANENT SUPPORTS Filed Sept. 28, 1942 LIGHTSENS/Tl VE /6ELAT/N LAVER- ATTACH/N6 LAYER OF CELLULOSE lY/TRATE 0RZE/N.

PAPER SUPPORT.

4 g 2 BY g Robert 1 Brown ATTORI'QEY.

Patented Jan. 8, 1946 TEMPORARY SUPPORT FOR PHOTOGRAPH- IC GELATINLAYERS AND METHOD OF TRANSFERRING SAME T PERMANENT SUPPORTS Rowland S.Potter, Brightford Heights, and Robert F. Brown, Rochester, N. Y.,assignors, by mesne assignments, to E. L du Pont de Nemours & Company,Wilmington, Del., a corporation of Delaware Application September 28,1942, Serial No. 459,898

' This invention relates to a temporary support for a photographicgelatin layer and method of transferring the gelatin layer to 'apermanent gelatin solution or the like, and thoroughly drying beforeremoving the temporary support. This is known as dry-stripping.

support, and has for its'purpose to afford a practical, economical andemcient structure by which a photographic light-sensitive or-othergelatin layer can be readily transferred from a term porary paper orother porous light weight, flexible support and aflixed to a glass,plastic, metal, wood, or other permanent surface or support beforeexposure and before developing and fixing the image, without requirin anadditional layer to hold the gelatin layer on the permanent support.thus enabling manufacturing such a product by applying a gelatin layeron a temporary support of paper and transferring only the gelatin layerquickly and easily to a metal, glass, plastic, wood, or lacqueredsurface to which it becomes permanently attached and-making it possibleto expose and process the light-sensitive gelatin layer after itstransfer to the permanent support.

In a more particular aspect, the invention has for its object to attacha, light-sensitive gelatin layer temporarily to a porous, light weight,flexible support of paper or other suitable material through theinstrumentality of an intermediate retaining layer or coatin that iswater permeable but insoluble in water or in any of the liquid mediumsused in effecting the transfer and remains permanently attached to thepaper support, the intermediate layer possessing a quality which enablesit to retain the gelatin layer attached to the paper support while dryand until it is desired to separate them and readily to release thegelatin layer when the latter is to be attached to the permanent supportsuch as glass, plastic, meta1, orwood, upon applying a water solution tosuch surface and squeegeeing the paper support and gelatin layerthereagainst with the gelatin layer adjacent to the water coveredsurface and then wetting. the back of the paper support, after which thepaper support with the permanently attached retaining layer can beremoved from the gelatin layer which remains firmly secured to thepermanent support without requiring any additional layer or coating andcan thereafter be exposed and processed, without having to remove anyadherent partially dissolved material of an intermediate layer.

Heretofore all methods of photographic layer stripping and transfer havedepended upon dissolving the attaching layer, or else included anattaching layer affording only limited adhesion with the gelatin layerwhen dry, the transfer being effected by firmly cementing the gelatinlayer to the permanent supp rt by means of a weak Of the types of layerswhich permit stripping by dissolving are those soluble in hot or coldwater, and those soluble in alkali or acid baths such as used inphotographic processing solutions.

An example of a photographic transfer layer which is held by a solubleinterlayer is disclosed in U. S. Patent No. 2,207,388 to Gerhard von iscoated over a water-permeable but water-insoluble layer which in turn iscoated on a paper support. The water-permeable layer is soluble in weakalkali, an acid, or neutral salt bath, and must be dissolved to releasethe light-sensitive gelatin layer from its temporary paper support whenit is desired to transfer it to a permanent support. It is necessary,therefore, to expose the light-sensitive layer before transfer since itis well known that the light-sensitiveness of such layers is easilyaffected by such In photome'chanical processes, especially in makingtemplates from drawings in the aircraft industries, it is necessary tomake absolutely accurate reproductions and to scrupulously avoiddistortions. Such distortions and inaccuracies cannot be avoided wherethe light-sensitive layer is exposed before transfer.

The present structure differs from all prior stripping films in that thesensitive gelatin layer can be stripped while wet from its temporarysupport and attached to the permanent support without the need of acollodion or other supporting layer that would remain attached to thegelatin layer, and may be exposed and processed after transfer to thepermanent support. This enable a substantial saving where large sizedsensitized glass plates'are required, since instead of carrying stocksof such sensitized plates in many sizes, the sensitized product is madein the form of paper, or other light weight, porous, flexible sheetsfrom which the gelatin layer can readilyebe transferred to a glass plateof any selected size, and after use the gelatin can be removed from theglass plate and the latter employed again for another gelatin layer. Theinvention also possesses great advantage in making large sized templatessuch as required in the airplane manufacturing industry and in otherlofting operations where it is desirable to attach a sensitized layer toa metal surface and expose it after attachment, which eliminatestheobvious difilculty of dimensional change which is undesirable whereaccurate drawings are neces The drawing is a sectional view of a photo!graphic paper made in accordance with a preferred embodiment of theinvention.

Referring more particularly to the drawing, in

carrying out the invention according to one possible procedure, asupport I of paper or other porous, light weight, flexible ,material isfirst coated in any well known manner with a thin and to release thegelatin layer when it is treated in the manner to be described presentlyto permit its transfer to the permanent support. The

photographic light-sensitive gelatin layer 8 isapplied by any of theconventional coating methods and any gelatin layer other than aphotographic light-sensitive layer, such as one adapted for draftingoperations, may be similarly applied, where it may be desirable totransfer such a gelatin layer from a temporary support to a permanentsupport.

Any suitable material having the necessary qualities may be employed forthis purpose, and it has been found that a thin layer of a celluloseester such as cellulose nitratecontaining a suitable porosity-givingagent when thoroughly dry, is water-permeable and also insoluble inwater or in any of the liquid mediums used in cfunprocessed, is thenfirmly squeegeed against the latter. Water is applied to the back of thepaper support, preferably after the squeegeeing operation, and the backof the paper is kept thoroughly wet thereafter. The sensitive gelatinlayer will firmly and quickly adhere to the liquid-covered supportingsurface after which the temporary or paper support can be pulled awayandthe gelatin layer alone remains attached to the permanent support,while the retaining layer of cellulose nitrate or other cellulose ester,zein, or other prolamine, remains permanently attached to the temporaryor paper support as it is pulled away from the gelatin layer. Thelightsensitive gelatin layer can then be exposed, and

processed in a manner well known in the photographic art with or withoutthe intermediate step of drying. 'Anyother gelatin layer can betransferred as described and used in-the manner for which it isintended.

. to produce, and more practical than any of the fecting the transfer,and will function properly to retain the sensitive gelatin layertemporarily attached to the paper support and to release the "gelatinlayer when it is to be transferred. any suitable porosity-giving agentsuch as urea may be incorporated in the cellulose nitrate layer.

A prolamine can also be employed for the purpose and one that has beenused successfully is zein which is a protein derived from corn andmarketed by the Corn Products Refining Company under the name Maaein."The zein is coated on the paper support as a solution which contains asuitable solvent mixture such as alcohol and water and which fallswithin the following general formula:

- Zein, 5% to by weight of total solution Alcohol, 85% to 95% by volumeof solvent mixture Water, 5% to by volume of solvent mixture.

This solution may contain a small quantity 'of wax, such as beeswax,carnauba, paraifin, or.

' supporting surface and then exposed and processed.

- To effect the separation-and transfer of the gelatin layer, the glass,plastic, metal, or other permanent surface is covered with water, whichmay or may not contain gelatin, gelatin chrome known types ofphotographic stripping layers.

While the invention has been described with reference to a certainstructure and procedure,

- the scope ofthe following claims.

alum, or chrome alum, in solution in a concentration generally usedinthe art as a cementing layer to the permanent support. The gelatinlayer, preferably We claim:

l. The combination with a temporary flexible paper support, of aphotographic light-sensitive gelatin layer which'can be transferred fromthe temporary support to a liquid-coated surface of a permanent supportby squeegeeing it thereon and applying water to the back of. the papersupport, and a retaining layer consisting of a prolamine between thetemporary support and the gelatin layer, said retaining layer beinginsoluble in water and the solutions used in transferring said gelatinlayer and acting to retain the gelatin layer on the temporary supportuntil it is to be transferred therefrom and then operable uponapplication of water to release it for attachment to the permanentsupport without adherence of any part of the retaining layer to thegelatin layer.

on the temporary support until it is to be transferred therefrom andthen operable upon application of water to release it for attachment tothe permanent support without adherenceof any part of the retaininglayerto the gelatin layer.

ROWLAND s. roam. ROBERT F. snows.

